1. Field of the Invention
The present invention relates to a polyolefinic resin and a composition comprising said resin, particularly a propylenic resin composition. More particularly, it relates to a polyolefinic resin and a composition comprising said resin having high heat resistance and excellent mechanical properties in a wide range of modulus, showing small temperature dependence of the mechanical properties and not causing stickiness on the surface of molded articles.
2. Description of the Related Arts
A polyolefinic resin is required to have a modulus varied in a wide range depending on application. Design of the resin, such as suitable selection of kind of olefin, was heretofore adjusted to satisfy the requirement for the wide range.
However, particularly when modulus of the resin is low, problems that characteristic mechanical properties of the resin are deteriorated and that stickiness of the surface of molded articles that is considered to be caused by the low molecular weight of the resin cannot be avoided are found depending on the temperature of application.
It is known that an excellent resin having a good balance of stiffness and impact strength at low temperature can be made of polypropylene resin in the form of block copolymer. However, an extremely large amount of a comonomer has to be contained in the copolymer to achieve very high impact strength at low temperature. It is inevitable that surface properties and heat resistance are significantly deteriorated by the extreme increase of the content of the comonomer even though impact strength is increased. Thus, improvement of these properties has been desired.
The present inventors developed soft polypropylene resins having specific structures before (Japanese Patent Application Laid Open Nos. 1991-14851 and 1991-168234). However, although these polypropylene resins have excellent mechanical properties as thermoplastic elastomers and heat resistance improved to some degree, improvement on (1) stickiness at the surface of polymer powder and molded articles during the production processes and (2) change of mechanical properties depending on temperature has been desired.